The Presbyterian Church (U.S.A.) will vote on two highly contentious issues at its General Assembly beginning Saturday with some presbyteries proposing reversal of the right to ordain openly gay and lesbian clergy and some seeking a change to the definition marriage.

Some presbyteries are calling for restoration of the 1996 standard that required "fidelity in the covenant of marriage between a man and a woman or chastity in singleness" for all clergy, according to PC(USA), which will have it biennial assembly from June 30-July 7 in Pittsburgh, Pa.

Some other presbyteries want to change the definition of marriage from being between "a man and a woman" to "two people." Five others are seeking an authoritative interpretation of the constitution that would allow pastors to officiate at wedding ceremonies in states where same-gender marriage is legal.

Proposals also include a call to confirm the current definition of marriage, and for a two-thirds vote from the presbyteries for any amendments to take effect.

The proposals come a year after a majority of the presbyteries ratified a constitutional amendment proposed by the 2010 General Assembly to remove the 1996 standard, a move that has resulted in the defection of at least 100 congregations from the denomination in recent years, according to the Presbyterian News Service.

"The marriage issue, depending how the vote goes, has the potential to be very, very distressing to some of our congregations," the Rev. Sheldon Sorge, pastor in the Pittsburgh Presbytery, told Desert News. "It would not surprise me at all if some congregations would see [approval of same-sex relationships] as the straw that broke the camel's back, for them to leave the denomination."

Jerry Deck, executive director of Presbyterian Global Fellowship, described the current atmosphere as tense.

"Though I have only been a Presbyterian for about ten years, I can certainly say that during that time I have never felt as much tension, anxiety and uncertainty surrounding a General Assembly as I feel now. Presbyterians on both sides of the aisle seem to be holding their breath, wondering what will happen, who will be unhappy, and whether or not a mass exodus from our denomination will quickly ensue."

Amendments and decisions of the assembly will have to be approved by a majority of the denomination's 173 presbyteries for it to be implemented.

"One thing that could pass is having the assembly issue an 'authoritative interpretation' of the constitution, which would say ... 'It's OK for Presbyterian ministers to officiate same-sex marriage if it is legal in the state where they are officiating,'" The Huffington Post quoted the Rev. Brian Ellison of Parkville Presbyterian Church near Kansas City, Mo., as saying.

In February, a church survey found that 51 percent of church members opposed gay marriage, while 34 percent approved. The others were undecided. The survey also showed that 41 percent of pastors approved of same-sex marriage, while 41 percent said they were against it.